Do products, which are advertised as “liquid carbon dioxide“, contain carbon or carbon dioxide?

No, since carbon is a solid (anthracite, diamond) at average ambient conditions (20 °C, 1 bar atmospheric pressure), whereas carbon dioxide is a gas which is only present in liquid form in pressurised gas cylinders (50 bar) under these conditions. Thus the products in these advertisements can neither contain carbon as an element nor carbon dioxide in liquid form.

But what do these products, advertised as „liquid carbon” for the aquarium, contain?

A simple test with one of these products shows that the active substance contained is glutaraldehyde (abbrev. glutaral) in a concentration of about 4 % as shown in the photo. After that we tested other products and found that the most common glutaraldehyde concentrations range from 1% to 4 %.

What is “glutaraldehyde“?

Glutaraldehyde is a disinfectant and is used industrially for various purposes, including in medicine, for example in dental practices. Glutaraldehyde is a dangerous substance in the aforementioned concentrations, and needs to be marked in accordance with EU directives.